168. Excel Sheet Column Title

problem

solution

class Solution {
public:
    string convertToTitle(int columnNumber) {
        string ret;
        while(columnNumber){
            int mod = (--columnNumber)%26;
            char c = mod+'A';
            ret = c+ret;
            columnNumber/=26;
        }
        return ret;
    }
};

analysis

• time complexity O(n)
• space complexity O(1)